Question

The accompanying figure shows reabsorption of some constituents of glomerular filtrate in different parts of mammalian nephron. What can these constituents be?

• A. $A-Na^{+}$, $B$-water, $C$-Urea
• B. $A$-Urea, $B-Na^{+}$, $C$-Water
• C. $A$-Water, $B-Na^{+}$, $C$-Urea
• D. $A-Na^{+}$, $B$-Urea, $C$-Water

Answer 1

Answer: (A)

Graph $A$ is for $Na^{+}$, as the $Na^{+}$ passes through proximal tubule, it's absorption increases. About $60\%$ of $Na^{+}$ from glomerular filtrate is absorbed here. Loop of Henle is divided into two parts: (i) Descending limb and (ii) Ascending limb. Descending limb is impermeable but ascending limb is permeable for $Na^{+}$. $Na^{+}$ reabsorption again increases in distal convoluted tubule under the influence of aldosterone. Its absorption also occur in collecting duct but it stabilises here. Graph $B$ is for water. Much of the water is absorbed in proximal tubule. Descending limb of loop of Henle is permeable but ascending limb of loop of Henle is impermeable to water. As the water passes through distal tubule and collecting duct its absorption increases. Graph C is for urea. Much of the urea is absorbed in proximal tubule. Descending limb is impermeable but ascending limb is partially permeable to urea. As it passes through distal and collecting tubule its absorption also increases.